This invention relates to a method of fractionating a mixture of high boiling carbonaceous material including normally solid carbonaceous material and mineral matter. In particular, supercritical and near supercritical fluids are used in extraction and fractionation of the materials.
Recent developments in the processing of fossil fuels have resulted in products and residua of extremely complex and intractable nature. This is especially true of the residua generated during coal liquefaction and various other processes involving heavy petroleum fractions, tarsands, shales, etc. Often such residua decompose prior to boiling and cannot be fractionated by conventional distillation processes.
In other developments, supercritical fluids have been used for extracting and fractionating organic substances. Representative of these developments are U.S. Pat. No. 3,969,196 to Zosel; U.S. Pat. No. 4,354,922 to Derbyshire et al.; U.S. Pat. No. 4,482,453 to Commes et al. and U.S. Pat. No. 4,502,944 to Nelson. These prior developments involve multi-step procedures in which process conditions of a supercritical fluid are varied to extract and separate product fractions. Even with this existing technology, there remains a need for improvements in separating and fractionating intractable, carbonaceous residua that also include solid mineral matter.
It is known that certain gas phases maintained near to supercritical conditions are capable of taking up large amounts of solutes from liquid or solid materials. When conditions such as temperature or pressure are reduced to below critical, a substantial decrease in solubility results. Also increases, particularly in temperature, to well above critical likewise reduce solubility in the supercritical gas. For purposes of this application, the terms "supercritical solvent", "supercritical phase", or "supercritical fluid" refer to a gas or gas mixture possibly with solute at or above critical temperature and critical pressure. The use of supercritical fluids to fractionate substances in a manner analogous to fractional distillation is termed "fractional destraction" in this application.